Rates of Reactions Flashcards
What is the rate of reaction?
Time taken for a certain reaction to occur
How is rate related to time?
Rate is inversely proportional to time
How does temperature affect reaction rate?
Higher temperature → particles gain kinetic energy → more frequent & successful collisions per unit time → increased reaction rate
How does concentration/pressure affect reaction rate?
Higher concentration/pressure → more reactant particles in a given volume → more successful collisions per unit time → higher reaction rate and more product formation
How does surface area affect reaction rate?
Increased surface area (smaller particle size) → more reactant molecules exposed → more successful collisions per unit time → increased reaction rate
What is a catalyst, and how does it affect reaction rate?
A substance that speeds up a reaction without being used up or changed. It provides an alternate pathway with lower activation energy
What steps should be followed to answer reaction rate questions?
- Identify the factor being tested
- Keep all other factors constant (controlled variables)
- Determine constant factors based on the state of matter:
- Aqueous solutions: Keep volume and concentration constant
- Solids: Keep mass and surface area constant
- Gases: Keep pressure and volume constant
How do you measure the increase in gas volume over time?
Use a gas syringe or upside-down measuring cylinder
Example reaction: CaCO₃ (marble chips) + excess HCl
* Add excess HCl to a conical flask
* Connect flask to a measuring cylinder via a delivery tube
* Add marble chips and seal flask with a rubber bung
* Measure gas volume produced over time
How do you measure the decrease in mass of reactants over time?
Use a balance to measure mass loss
Method:
1. Weigh an empty conical flask
2. Add reactants and measure immediate mass
3. Cover the flask with cotton wool (allows gas to escape while preventing splashing)
4. Regularly measure mass per unit time
How do you measure the time for a substance [X] to disappear?
Used for reactions with color change
Method:
1. Draw [X] on a white sheet
2. Place a beaker with reactants over [X]
3. Start the stopwatch when reactants are mixed
4. Stop the stopwatch when [X] is no longer visible
What are errors in the “disappearance of [X]” experiment?
- Beaker shape: A shallow beaker takes longer for [X] to disappear
- Subjectivity: Difficulty in defining exactly when [X] is no longer visible
When is a reaction considered complete?
When bubbling or color change stops
What factor affects both reaction rate and product amount?
Concentration/pressure
